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(单词翻译:双击或拖选)
You might think frogs catch insects ‘cause their tongues are sticky. "But why is the tongue sticky, and how does it actually adhere to these insects at these very high accelerations1?"
Those are the questions Alexis Noel, a PhD candidate in mechanical engineering at Georgia Tech, wanted to answer. So she and her team got frog tongues from a dissection2 lab, and tested their consistency3. Ten times softer than human tongues. A texture4 more like brain tissue. "Their tongue is very much like a sponge. It's infused with this thick, viscous5 saliva6."
That saliva was their next study subject. "And in order to test the saliva we had to get about a fifth of a teaspoon7 of fluid. Which is a lot of saliva, in a frog's case." They put the saliva in a rheometer, a tool that can measure viscosity8. And they found that frog saliva is what's called a 'shear9-thinning fluid'—its viscosity changes, depending on conditions.
You might be more familiar with a different shear-thinning fluid. "Ketchup10. When you smack11 the bottom of the ketchup bottle you're actually invoking12 shear forces within the ketchup itself. And ketchup, because it's shear thinning, its viscosity actually drops and allows it to slide out of the bottle easily."
So back to our frogs: the tongue shoots out, hits the bug13 and deforms14 around it. That impact is like a smack on a ketchup bottle—it changes the saliva from thick and sticky to more watery15, free to flow all over the bug. Then the tongue bounces back, like a bungee cord, and the saliva thickens up again. What's next is beyond weird16.
"Frogs actually take their bulbous eyeballs and bring them down into their mouth cavity and use their eyeballs to shove the insect down the throat." That force turns the saliva watery again, "and the insect slides down the gullet." The study is in the Journal of the Royal Society Interface17. [Alexis C. Noel et al., Frogs use a viscoelastic tongue and non-Newtonian saliva to catch prey]
With the case closed on this one, Noel's next inquiries18 are on grippy fingertips. The dust-collecting properties of earwax. And—wait for it—cat tongues. "Yeah, I get paid to watch cat videos all day."
—Christopher Intagliata
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1
accelerations
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n.加速( acceleration的名词复数 );加速度;(车辆)加速能力;(优秀学生的)跳级 | |
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2
dissection
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n.分析;解剖 | |
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3
consistency
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n.一贯性,前后一致,稳定性;(液体的)浓度 | |
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4
texture
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n.(织物)质地;(材料)构造;结构;肌理 | |
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viscous
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adj.粘滞的,粘性的 | |
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6
saliva
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n.唾液,口水 | |
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7
teaspoon
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n.茶匙 | |
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8
viscosity
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n.粘度,粘性 | |
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9
shear
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n.修剪,剪下的东西,羊的一岁;vt.剪掉,割,剥夺;vi.修剪,切割,剥夺,穿越 | |
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10
ketchup
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n.蕃茄酱,蕃茄沙司 | |
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smack
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vt.拍,打,掴;咂嘴;vi.含有…意味;n.拍 | |
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12
invoking
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v.援引( invoke的现在分词 );行使(权利等);祈求救助;恳求 | |
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bug
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n.虫子;故障;窃听器;vt.纠缠;装窃听器 | |
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deforms
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使变形,使残废,丑化( deform的第三人称单数 ) | |
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15
watery
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adj.有水的,水汪汪的;湿的,湿润的 | |
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16
weird
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adj.古怪的,离奇的;怪诞的,神秘而可怕的 | |
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17
interface
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n.接合部位,分界面;v.(使)互相联系 | |
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18
inquiries
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n.调查( inquiry的名词复数 );疑问;探究;打听 | |
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